1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus provided with the electrophotographic photosensitive member. In more detail, the present invention relates to an electrophotographic photosensitive member having a surface layer containing a specified resin, and a process cartridge and an electrophotographic apparatus provided with the electrophotographic photosensitive member.
2. Description of the Related Art
Electrophotographic photosensitive members (OPC photosensitive members) containing organic photoconductive compounds have been aggressively developed in the recent years. For example, U.S. Pat. No. 3,837,851 discloses a photosensitive member provided with a charge transfer layer containing triarylpyrazoline, while U.S. Pat. No. 3,871,880 discloses a photosensitive member provided with a charge generation layer containing perylene pigment derivatives and a charge transfer layer containing condensates of 3-propylene and formaldehyde.
Each of the organic photoconductive compounds has a different photosensitive wavelength region depending on the species of the compound. For example, Japanese Patent Laid-Open Nos. 61-272754 and 56-167759 disclose azo pigments having a high sensitivity in the visible region and Japanese Patent Laid-Open Nos. 57-19576 and 61-228453 disclose compounds having a high sensitivity in the infrared region.
Among these compounds, those having a high sensitivity in the infrared region have been used for laser beam printers and LED printers.
Meanwhile, the electrophotographic photosensitive member is naturally required to possess a proper sensitivity, electrical characteristic and mechanical characteristic in addition to optical characteristic to comply with the applied electrophotographic process.
Especially, since electrical and mechanical stresses are directly and repeatedly impressed to the electrophotographic photosensitive member for repeated use, durabilities against these stresses are also required.
For example, durabilities against chemical deterioration by ozone and nitrogen oxides generated during charging or against electrical and mechanical degradation such as surface abrasion and flaw caused by discharge and cleaning are required.
The OPC photosensitive member is in particular composed of a substance so soft as compared with inorganic photosensitive members that durability against mechanical degradation is especially needed.
The foregoing problems evidently occurs in the contact charging method being developed as a leading technology in recent years and disclosed in Japanese Patent Laid-Open Nos. 57-17826 and 58-40566, wherein the electrophotographic photosensitive member is charged by impressing a voltage on a charging member disposed in direct contact with the electrophotographic photosensitive member. This contact charging method has several advantages such as generating extremely small amounts of ozone as compared with scorotrons or being very economical without waste electricity in contrast to scorotrons in which about 80% of the current fed to a charger flows through the shield.
However, an improved mechanical strength is required for the electrophotographic photosensitive member because the charging member makes a direct contact with the electrophotographic photosensitive member. It is proposed, on the other hand, to use a voltage in which a direct current (DC) voltage is superimposed on an alternating current (AC) voltage as an impressed voltage in order to improve charging stability since the contact charging method also depends on charging by discharge (Japanese Patent Laid-Open No. 63-149668).
Although this charging method enables one to improve charging stability, use of the AC voltage increases the amount of electric current flowing through the electrophotographic photosensitive member. Accordingly, the amount of abrasion of the electrophotographic photosensitive member may increase. As hitherto described, not only mechanical strength but also electrical strength, along with durability against solvent cracks caused by adhesion of a mechanical oil and hand grease, are required for the electrophotographic photosensitive member.